Folded cardboard containers are known in which the inside of the container is covered with a layer of thermoformed synthetic material and in which the container has upper edges formed into a rim.
The rim provides a reinforcement of the circumference of the container (which may be in the shape of a dish) and a surface for receiving a cover. The cover may be fixed to the rim by gluing or heat joining.
This type of packaging is normally used for receiving food products, some of which are liquid. It is therefore necessary for the containers to be fluid tight, which means that the layer of synthetic material is uniformly spread over, without any irregularity, on the bottom, at the walls and on the rim. It is truly important that there be no hole in the layer because the container itself does not have the same quality of tightness as the synthetic material. In addition, it is indispensible that the rim be perfectly plane since it is intended for receiving the cover, the fixing of which is an essential element of the tightness of the container.
It is very difficult to obtain upper edges in a regular, uniform and industrially feasible way. As a matter of fact, to obtain an economical container, it is necessary to form the body of the container from cut and grooved blanks which can be stored flat and to use a very thin synthetic material. This structure is capable of being assembled by low-cost totally automatic means or by manual labor, by thermo-forming of the synthetic layer onto a die in which the cardboard blank is placed, and kept, while covered by the layer which is attached to the entire surface.
To obtain a container of this type, a cardboard blank is used which is cut and grooved. It is flat and is put in the desired form by at least two inverse folds for each face, i.e. a fold toward the upper part of the wall relative to the bottom, and a fold of the edges toward the bottom with respect to the upper end of the walls.
As explained above, it is necessary that the edges constitute a rim which is completely plane for esthetic reasons, to avoid obstruction in stockpiling and to attain perfection in covering the container.
In spite of the improvements carried out by the applicants themselves, as disclosed in the French Patent Application No. 77/29714 of Oct. 3, 1977, the attainment of such a platform remains a difficult operation, i.e. with respect to manufacturing, because for a hundred containers made, a few are found which must be reworked due to faults in joining and lowered edges.
Also known is German Pat. No. 1.486.954 which relates to a package comprising a frame in one piece and walls jointed on this frame. The package disclosed in the German Patent, however, neither comprises the bottom nor the continuous cardboard wall and, as seen in particular in FIG. 2, the cardboard portions are the frame and the walls, whereas the bottom and the walls are made of synthetic material.
In German Pat. No. 2.036.082, a cardboard box is described which comprises a detachable portion of double walls being placed between the walls of the actual box and the inner walls resulting from the cutting and folding of the bottom which, for this reason, does not exist any more.
These arrangements differ substantially from those of the present invention with respect to numerous points, i.e.:
1. The bottom of such a package is added and is not part of any of the elements previously described.
2. The upper and lower walls, respectively, are not aligned in the normal manner which is in the same plane, but are so placed that the ones are behind the others, in four thicknesses for each side altogether.
3. The upper and lower portions are not interconnected.
4. The upper and lower portions are only united by means of a third element which is another cardboard container having gluing flanges and a jointed cover.